The subject of the present invention is a motorized reduction gear, particularly for driving vehicle equipment, of the type comprising a rotor equipped with a rotor shaft, a reduction gearbox which contains an endless screw in mesh with a gearwheel containing a damper together with means of sealing the box, and an output member rotated by the damper.
Reduction gearboxes of current motorized reduction gears comprise the following parts: gearwheel, hub, lip seal, cover and plastic drum onto which a cable, for example a window-lifter cable, can be wound or a pinion made of sintered steel and an overmoulded plastic hub.
This structure contains a relatively high number of parts, and this leads to a relatively high cost of manufacture.
Furthermore, there is axial play in the line of shaft mounted in the motorized reduction gear. This axial play is due to the combination of spread on the dimensions of the various parts on assembly (shaft, stop, box, case, etc.), these various parts placed end to end being shorter than their housings.
Hitherto, this axial play has been compensated for manually using a screw housed in the end of the box facing the rotor shaft hole, and which is locked by an adhesive which at the same time provides a seal. This adjustment process takes a long time and is therefore expensive and increases the cost of manufacture of the motorized reduction gear.
U.S. Pat. No. 5,169,245 describes a motorized reduction gear in which the axial play is compensated for by a coil spring exerting an axial thrust on the end of the rotor shaft, with the insertion of a part which can come into abutment against a shoulder of the box when the spring has been compressed by a given amount. In such a device, the spring compresses underxe2x80x94the effect of the axial force and, when the direction of rotation of the motorized reduction gear is reversed, the energy stored up in the spring is suddenly released. Thus, the opposite end of the rotor shaft is pressed violently against the end of the stator, and this causes a very annoying noise.
Finally, another problem is the result of a ring being crimped between the shaft of the motorized reduction gear and the stator. This is because the inside diameter of this ring varies as a result of the irregularities of the diameter of its housing in the end of the stator. Thus, the radial clearance between the shaft and the ring has irregularities, and these cause annoying shaft oscillations.
The object of the invention is to produce a motorized reduction gear whose structure is simplified compared with the known motorized reduction gears and which is therefore of a lower cost of manufacture.
The invention also sets out to obtain better control over the inside diameter between the rotor shaft and the ring inserted between it and the stator, in order to reduce the shaft oscillations.
Another object of the invention is to produce automatic compensation for the axial play of the line of shafts in the motorized reduction gear using means which are simple, effective and inexpensive and which furthermore run no risk of damaging the adjustment device.
In accordance with the invention, the sealing means comprise an annular wall of the gearwheel and a seal arranged between the said wall and the wall of the box, and this seal is secured either to the box and resting with sliding on the annular wall or to the annular wall and resting with sliding on the box, sealing being achieved between at least one lip of the seal and the said annular wall.
According to one feature of the invention, the damper is made as one piece, has peripheral cut-outs designed to accommodate, on the one hand, radial fins of the wheel and, on the other hand, elements for driving an output member, and the edges of the cut-outs are chamfered.
According to one embodiment of the invention, the damper is equipped on at least one of its faces with means of centring in a cavity delimited between the wheel and the output member and for leaving the volume needed for the damper to expand when compressed.
The chamfers on the damper have a two-fold advantage: on the one hand, they ensure that the angular deflection of the damper as a function of the torque is gradual and, on the other hand, they make the damper easier to fit automatically onto the hub of the gearwheel.
According to another feature of the invention, the motorized reduction gear comprises an output member which consists of a drum coaxial with a damper, with the seal, and with the gearwheel, the damper being housed in the wheel and secured to it so that they rotate as one; the drum is intended to receive a cable, particularly for a window-lifter of the cable-operated type; it being possible for this drum to be equipped with means for securing it to the damper so that the two rotate as one.
These securing means may consist of the fingers of the drum which cooperate with the damper.
Thus, the damper itself drives the drum directly instead of the intermediate plastic hub, which can be omitted, this reducing the number of parts in the system.
According to another feature of the invention, the output member is a pinion made as a single piece with a hub inside the gearwheel, preferably made of sintered steel. This one-piece embodiment of the pinion and of the hub reduces the cost of manufacture compared with the cost of the corresponding earlier parts which were obtained by overmoulding the hub onto the sintered pinion.
According to another specific feature of the invention, the means for automatically adjusting the axial play comprise a damping stop made of an elastomeric material and a metallic washer embedded in this stop and against which the end of the shaft bears with preload in order to automatically compensate for the axial play.
This stop system makes it possible to limit to a predetermined value the axial compressive load experienced by the damper when the motorized reduction gear is in operation.
Furthermore, the fact of using an elastomeric damper rather than a coil spring avoids the drawbacks associated with the latter. Indeed, an elastomeric element has the property of absorbing some of the energy or deformation by internal friction between the molecular chains of the elastomeric material. This absorption of some of the energy generated by the bearing force makes it possible to considerably reduce the loudness of the annoying noise when the motor direction reverses.
The maximum force experienced by the damper may, for example, be 100 newtons, in accordance with the standards in force. Beyond this value, the axial force developed by the rotor shaft during the operation of the motorized reduction gear is exerted on the wall of the box via the stop system, and this avoids any possibility of the damper being damaged by an excessive axial force.
The rigid stop is advantageously fitted with a means for preventing it from rotating about the axis of the rotor shaft.